Successful treatment of cancer by neutron therapy necessitates a knowledge of the degree of risk of normal tissue sequelae associated with the cure of the tumor. This will be expressed as the ratio of the amount of photon irradiation which results in several specific late effects to the amount of neutron irradiation which results in the same specific effects (RBE values). The aim of this investigation will be to obtain these values for sequelae in the brain, spinal cord and lung. Currently fast neutrons are being used by the Middle Atlantic Neutron Therapy Association (as well as several other centers) in the treatment of cancer patients which include the brain, spinal cord and lung within the treatment area. No animal data are available on the chronic effects of the MANTA beam on these organs, nor has a comparable investigation been performed elsewhere. Experiments based on a pilot study have been designed to investigate the late effects of 15 MeV neutrons on these organs in beagles. This proposal, using the same fractionation schedule used clinically, will evaluate the sequelae utilizing functional and quantitative methods. Late effects on brain and cord will be measured by quantitative studies including neurological function examination, sensory and visual evoked responses, onset of neurological deficits (paresis, paralysis) and quantitative histopathological studies. Late effects on lung tissue will be measured by respiratory mechanics including lung volumes, compliance, resistance, closing volumes, and pulmonary diffusion capacity as well as quantitative histopathologic studies. Radio-nuclide evaluation of pulmonary function will be obtained through regional ventilation, perfusion, and ventilation- perfusion ratios, and radioaerosol clearance. Previous evaluations of sequelae of neutron therapy have failed to use clinical exposure schedules or to employ quantitative methodology subject to statistical analysis.